Chapter 15: Atmospheric Optics Fig. 15-CO, p. 414 Sunlight bending through ice crystals in cirriform clouds produces bands of color called sundogs, or parhelia, on both sides of the sun on this cold winter day in Minnesota. Photo © 2002 STAR TRIBUNE/Minneapolis-St. Paul. Fig. 15-CO, p. 414

White Clouds and Scattered Light reflection scattering Thunderstorms appear dark because the clouds (cumulonimbus) are about 10 km deep, scattering most of the light.

Figure 15.1: Cloud droplets scatter all wavelengths of visible white light about equally. The different colors represent different wavelengths of visible light. Cloud droplets scatter all wavelengths of visible white light about equally. The different colors represent different wavelengths of visible light. Fig. 15-1, p. 417

Figure 15.2: Since tiny cloud droplets scatter visible light in all directions, light from many billions of droplets turns a cloud white. Since tiny cloud droplets scatter visible light in all directions, light from many billions of droplets turns a cloud white. Fig. 15-2, p. 417

Figure 15.4: The sky appears blue because billions of air molecules selectively scatter the shorter wavelengths of visible light more effectively than the longer ones. This causes us to see blue light coming from all directions. The sky appears blue because billions of air molecules selectively scatter the shorter wavelengths of visible light more effectively than the longer ones. This causes us to see blue light coming from all directions. Fig. 15-4, p. 418

crepuscular rays Figure 15.7: The scattering of sunlight by dust and haze produces these white bands of crepuscular rays. The scattering of sunlight by dust and haze produces these white bands of crepuscular rays. Fig. 15-7, p. 419

Figure 15.8: Because of the selective scattering of radiant energy by a thick section of atmosphere, the sun at sunrise and sunset appears either yellow, orange, or red. The more particles in the atmosphere, the more scattering of sunlight, and the redder the sun appears. Because of the selective scattering of radiant energy by a thick section of atmosphere, the sun at sunrise and sunset appears either yellow, orange, or red. The more particles in the atmosphere, the more scattering of sunlight, and the redder the sun appears. Fig. 15-8, p. 420

The behavior of light as it enters and leaves a more-dense substance, such as water. Figure 15.11: The behavior of light as it enters and leaves a more-dense substance, such as water. Fig. 15-11, p. 421

Figure 15.12: Due to the bending of starlight by the atmosphere, stars not directly overhead appear to be higher than they really are. Fig. 15-12, p. 422

The Mirage Inferior mirage Figure 15.15: The road in the photo appears wet because blue skylight is bending up into the camera as the light passes through air of different densities. Inferior mirage The road in the photo appears wet because blue skylight is bending up into the camera as the light passes through air of different densities. Fig. 15-15, p. 424

Figure 15.16: Inferior mirage over hot desert sand. The road in the photo appears wet because blue skylight is bending up into the camera as the light passes through air of different densities. Fig. 15-16, p. 424

superior mirage Figure 15.17: The formation of a superior mirage. When cold air lies close to the surface with warm air aloft, light from distant mountains is refracted toward the normal as it enters the cold air. This causes an observer on the ground to see mountains higher and closer than they really are. The formation of a superior mirage. When cold air lies close to the surface with warm air aloft, light from distant mountains is refracted toward the normal as it enters the cold air. This causes an observer on the ground to see mountains higher and closer than they really are. Fig. 15-17, p. 425

Figure 15.18: A 22° halo around the sun, produced by the refraction of sunlight through ice crystals. A 22° halo around the sun, produced by the refraction of sunlight through ice crystals. Fig. 15-18, p. 425

The formation of a 22° and a 46° halo with column-type ice crystals. Figure 15.19: The formation of a 22° and a 46° halo with column-type ice crystals. Fig. 15-19, p. 426

Halo with an upper tangent arc Figure 15.20: Halo with an upper tangent arc. Fig. 15-20, p. 427

Refraction and dispersion of light through a glass prism. Figure 15.21: Refraction and dispersion of light through a glass prism. Fig. 15-21, p. 427

Platelike ice crystals falling with their flat surfaces parallel to the earth produce sundogs. Figure 15.22: Platelike ice crystals falling with their flat surfaces parallel to the earth produce sundogs. Fig. 15-22, p. 427

The bright areas on each side of the sun are sundogs. Figure 15.23: The bright areas on each side of the sun are sundogs. Fig. 15-23, p. 428

A brilliant red sun pillar extending upward above the sun, produced by the reflection of sunlight off ice crystals. Figure 15.24: A brilliant red sun pillar extending upward above the sun, produced by the reflection of sunlight off ice crystals. Fig. 15-24, p. 428

Optical phenomena that form when cirriform ice crystal clouds are present. Figure 15.25: Optical phenomena that form when cirriform ice crystal clouds are present. Fig. 15-25, p. 429

When you observe a rainbow, the sun is always to your back. Figure 15.26: When you observe a rainbow, the sun is always to your back. In middle latitudes, a rainbow in the evening indicates that clearing weather is ahead. Fig. 15-26, p. 429

Rainbows Sunlight internally reflected and dispersed by a raindrop. The light ray is internally reflected only when it strikes the backside of the drop at an angle greater than the critical angle for water. (b) Refraction of the light as it enters the drop causes the point of reflection (on the back of the drop) to be different for each color. Hence, the colors are separated from each other when the light emerges from the raindrop.

Figure 15.27: Sunlight internally reflected and dispersed by a raindrop. (a) The light ray is internally reflected only when it strikes the backside of the drop at an angle greater than the critical angle for water. (b) Refraction of the light as it enters the drop causes the point of reflection (on the back of the drop) to be different for each color. Hence, the colors are separated from each other when the light emerges from the raindrop. Fig. 15-27, p. 430

The formation of a primary rainbow The formation of a primary rainbow. The observer sees red light from the upper drop and violet light from the lower drop. Figure 15.28: The formation of a primary rainbow. The observer sees red light from the upper drop and violet light from the lower drop. Fig. 15-28, p. 430